This invention relates to arrangements for testing and facilitating adjustment of telecommunication repeaters of the medium speed digital line regenerator type and in particular to an arrangement for testing a repeater installed in a telephone line.
Digital regenerators or repeaters are employed in digital transmission systems to receive, amplify and reshape the pulses of the code being transmitted. Generally such transmission systems employ a ternary code, i.e. the information is coded into a series of positive and negative going pulses. The regenerator receives the attenuated pulse code signals from the line, filters out noise and other spurious signals and generates a stream of pulses at its output to recover the original code transmission. Such regenerators require testing to ensure correct operation, e.g. the repeater must not miss pulses of the input code, nor must it generates spurious pulses.
The ternary pulse codes used with digital transmission are generally of the pseudo-random type. Over a sufficiently long interval there are equal numbers of positive and negative going pulses. Furthermore, even over a short interval there is, depending on the particular code employed, a maximum possible disparity between positive and negative going pulses. Incorrect operation of the repeater will thus result in a disparity between positive and negative pulses beyond these limits.
A suitable digital code which may be used for such transmission is the 4B3T code described in U.S. Pat. Nos. 3,611,141 and 3,646,517 whose disclosures are incorporated herein by reference. The disparity between positive and negative pulses of this code, which provides a method of encoding four-bit binary words into three-bit ternary words, cannot exceed four for correct operation. Other codes which may also be employed, for example, an alternate mark inversion code having a maximum cummulative disparity of one, or a triple ternary code having a maximum cummulative disparity of three.